The 258mm based converter takes over where the 245mm units leave off. I generally point folks making over 850ftlbs or 3600lbs vehicle weight to the 258. There is some room for opinion here. I often put folks with big rims, off road applications or other considerations into the 258mm. These have a tendency to drive more “factory” than the smaller units.
The 258 is the core of choice for most modern converter companies at power levels over 850ft lbs of torque. There are 3 different factory impeller (pumps) and 4 different OEM stators, so the power range and stall speed is very adjustable even before we get to the aftermarket stators available (of which there are nearly 2 dozen)
Every unit is fully furnace brazed THEN hand tig brazed reinforcements are added.
Because the 258 is likely to see such high power, I recommend considering a swap to a mechanical diode. This replaces the factory roller clutch with a much stronger assembly. I have detailed pictures below.
I now also offer spragless stator insert upgrades for both the 400 (normal shaft and the various big shaft sizes and the 4L80) Keep in mind while this is ultimate stator sprag strength, it makes a lot of heat. You will be responsible for shedding that extra 50+ degrees of temp to keep your transmission alive. These are about the only thing to be done for rock bouncers that have any chance of living. Stall speed is not affected by this no matter who is spreading that rumor.
As of May 2026 my 4L80e 258 prices are $1175 for 4L80 single billet oem stator, $1250 for triple disc OEM stator, add $550 for mechanical diode. Spragess upgrade is 375.
Turbo 400 258mm price $1025, add diode $550, sprag delete $375
Every 258 converter I build is fully furnace brazed and then tig braze reinforced throughout, billet cover, anti-ballon plated impeller and is balanced separately as parts, and then finally as an assembly. My converter build quality is at a level that rivals some of the biggest names on the market. Far beyond the average off the shelf unit from the three letter acronym guys. And I’m able to keep costs very reasonable as I have a much lower overhead cost.
I can also converter any 258 to bolt together for $1000 additional parts and labor
I generally do not shelf stock these as application and configuration can vary so much. Please call or text 503 560 1852 or email me truckdoug@The4L80eGuy.com to discuss your needs.
The 258mm based converter takes over where the 245mm units leave off. I generally point folks making over 850ftlbs or 3600lbs vehicle weight to the 258. There is some room for opinion here. I often put folks with big rims, off road applications or other considerations into the 258mm. These have a tendency to drive more “factory” than the smaller units.
The 258 is the core of choice for most modern converter companies at power levels over 850ft lbs of torque. There are 3 different factory impeller (pumps) and 4 different OEM stators, so the power range and stall speed is very adjustable even before we get to the aftermarket stators available (of which there are nearly 2 dozen)
Every unit is fully furnace brazed THEN hand tig brazed reinforcements are added.
Because the 258 is likely to see such high power, I recommend considering a swap to a mechanical diode. This replaces the factory roller clutch with a much stronger assembly. I have detailed pictures below.
I now also offer spragless stator insert upgrades for both the 400 (normal shaft and the various big shaft sizes and the 4L80) Keep in mind while this is ultimate stator sprag strength, it makes a lot of heat. You will be responsible for shedding that extra 50+ degrees of temp to keep your transmission alive. These are about the only thing to be done for rock bouncers that have any chance of living. Stall speed is not affected by this no matter who is spreading that rumor.
As of May 2026 my 4L80e 258 prices are $1175 for 4L80 single billet oem stator, $1250 for triple disc OEM stator, add $550 for mechanical diode. Spragess upgrade is 375.
Turbo 400 258mm price $1025, add diode $550, sprag delete $375
Every 258 converter I build is fully furnace brazed and then tig braze reinforced throughout, billet cover, anti-ballon plated impeller and is balanced separately as parts, and then finally as an assembly. My converter build quality is at a level that rivals some of the biggest names on the market. Far beyond the average off the shelf unit from the three letter acronym guys. And I’m able to keep costs very reasonable as I have a much lower overhead cost.
I can also converter any 258 to bolt together for $1000 additional parts and labor
I generally do not shelf stock these as application and configuration can vary so much. Please call or text 503 560 1852 or email me truckdoug@The4L80eGuy.com to discuss your needs.
